The invention relates to a turbocharger having a swing vane nozzle assembly, and a method for manufacturing a turbocharger,
The invention can be applied in heavy-duty vehicles, such as trucks, buses and construction equipment. Although the invention will be described with respect to a truck, the invention is not restricted to this particular vehicle, but may also be used in other applications utilizing turbocharger units such as aero or marine systems.
A turbocharger unit is a vehicle component used together with an associated internal combustion engine, typically a diesel engine. The turbocharger unit is configured to recover a part of the energy of the exhaust gas and to use that energy to compress intake air flowing into the combustion chamber of the internal combustion engine. Turbocharger units are commonly provided for increasing the efficiency and power of the internal combustion engine.
A turbocharger unit has three main components; a turbine for converting energy of the exhaust gas flow to a rotational movement of the turbine, a compressor rotationally connected to the turbine for compressing intake air, and a housing enclosing the turbine and the compressor as well as a rotating shaft, bearings, etc.
Some turbochargers are provided with a swing vane nozzle assembly. Such turbochargers, also known as variable geometry turbochargers (VGTs) allow the intake airflow to be controlled and thereby optimized over a range of engine speeds. A VGT may for this purpose be provided with a plurality of inlet guide vanes on the turbine stator. An inlet passage to the turbine has a circumferential extension around the turbine and forms an annular passageway. The inlet guide vanes on the turbine stator are arranged circumferentially spaced in this passage. The intake airflow is optimized by changing the angle of the inlet guide vanes on the turbine stator. An optimal position for the inlet guide vanes is determined from a combination of desired torque response, fuel economy, and emission requirement. More specifically, the annular passageway is connecting a scroll shaped volute defined in the turbine housing to a turbine chamber where the turbine is located.
The inlet guide vanes are arranged between a front nozzle ring and a rear nozzle ring, such that the swing vane nozzle assembly, comprising the nozzle rings and the inlet guide vanes, is arranged radially outside the turbine. For efficiency reasons it is desired to have a very small axial clearance between the inlet guide vanes and the nozzle rings. Due to such small clearance any distortion of the nozzle rings must be prevented in order to reduce the risk for sticking of the inlet guide vanes.
An important aspect of VGT's is thus how to attach the swing vane nozzle assembly in order to avoid the distortion of the nozzle rings and to minimize heat inflow into the bearing housing. Too high heat inflow can lead to oil coking problems for the bearings.
JP2010196653 describes a swing vane nozzle assembly wherein a first nozzle ring is guided axially at its outer periphery, and guided radially at its inner periphery. The second nozzle ring is radially guided at its inner periphery, and a radial step of the turbine housing provides an axial guidance for the inner periphery of the second nozzle ring. The solution described in the prior art document however suffers from the disadvantage that deformations, or distortion of the nozzle rings may occur due to a difference in thermal expansion of the bearing housing, guiding the first nozzle ring, and the turbine housing guiding the second nozzle ring.
It is desirable to provide a turbocharger overcoming the above mentioned drawback of prior art turbochargers.
Since the inner periphery of the front nozzle ring is arranged at a distance from the bearing housing, no radial guidance of the front nozzle ring is provided. The swing vane nozzle assembly may therefore withstand thermal expansions with a reduced risk for sticking of the inlet guide vanes.
A turbocharger having a swing vane nozzle assembly is therefore provided. The turbocharger comprises a turbine housing and a bearing housing, and the swing vane nozzle assembly is configured to control an exhaust gas flow to a turbine arranged inside the turbine housing. The swing vane nozzle assembly comprises a front nozzle ring, a rear nozzle ring, and a plurality of pivotable gas flow control vanes arranged between the front nozzle ring and the rear nozzle ring. The rear nozzle ring is radially guided by the turbine housing, while a radially outer portion of the front nozzle ring is clamped between the bearing housing and the turbine housing thus forming an axial guidance of the front nozzle ring. An inner periphery of the front nozzle ring is arranged at a distance from the bearing housing.
In an embodiment, the turbocharger comprises a heat shield being arranged between the bearing housing and the inner periphery of the front nozzle ring. Since there is a radial gap between the bearing housing and the inner periphery of the front nozzle ring, the turbocharger allows for a very simple and robust heat shield.
In an embodiment the heat shield has an annular shape having a radially inner portion and a radially outer portion, the outer portion being axially displaced relative the inner portion. The outer portion of the heat shield may be axially displaced in a direction towards a turbine arranged inside the turbine housing, and the outer portion of the heat shield, may seal against the from nozzle ring. The heat shield may thus be attached to the bearing housing in a very simple way, while it achieves the desired shielding properties by isolating the bearing housing and its associated components from the heat of the exhaust gases.
In an embodiment the interface between the bearing housing and the turbine housing forms a recess in which the radially outer portion of the front nozzle ring is received. Clamping of the front nozzle ring is therefore easily achieved. The width of the recess may be slightly larger than the width of the radially outer portion of the front nozzle ring such that the axial guidance is formed by a light clearance fit.
In an embodiment, the turbocharger comprises a spring, such as a plate spring, arranged between the bearing housing and the radially outer portion of the front nozzle ring. The spring may thus provide an axial prestress to the front nozzle ring.
In an embodiment the turbocharger further comprises a seal arranged between the turbine housing and the inner periphery of the rear nozzie ring for further improving the radial guidance of the swing vane nozzle assembly. The seal may in some embodiments be an O-ring.
An exhaust aftertreatment system for an internal combustion engine is also provided. The exhaust aftertreatment system comprises at least one turbocharger according to the first aspect.
A vehicle is also provided. The vehicle comprises an exhaust aftertreatment system according to the second aspect.
A method for manufacturing a turbocharger with a swing vane nozzle assembly is also provided. The swing vane nozzle assembly has a front nozzle ring, a rear nozzle ring, and a plurality of pivotable gas flow control vanes arranged between the front nozzle ring and the rear nozzle ring. The method comprises the steps of: arranging the rear nozzle ring onto a cylindrical portion of a turbine housing such that the rear nozzle ring is radially guided by the turbine housing, and arranging a radially outer portion of the front nozzle ring between a bearing housing and the turbine housing thus forming an axial guidance of the front nozzle ring. The step of arranging the radially outer portion of the front nozzle ring is performed such that an inner periphery of the front nozzle ring is arranged at a distance from the bearing housing.
In an embodiment the method further comprises the step of providing a heat shield between the bearing housing and the inner periphery of the front nozzle ring. This step may be performed such that the outer portion of the heat shield seals against the front nozzle ring.
In an embodiment the method further comprises the step of arranging a spring between the bearing housing and the radially outer portion of the front nozzle ring.
In an embodiment the method further comprises the step of arranging a seal between the turbine housing and the inner periphery of the rear nozzle ring.
In an embodiment the steps of arranging the rear nozzle ring onto a cylindrical portion of a turbine housing, and arranging a radially outer portion of the front nozzle ring between a bearing housing and the turbine housing are performed by positioning the swing vane nozzle assembly in the bearing housing, and thereafter arranging the turbine housing in the correct position relative the bearing housing. In such embodiment, the step of arranging the heat shield may be performed before the step of positioning the swing vane nozzle assembly in the bearing housing.
Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.